Battling those bloodsucking summer pests

Sunday

May 26, 2013 at 12:01 AMMay 26, 2013 at 1:00 AM

Worldwide, more than 3,000 species of mosquitoes are making nuisances of themselves, sucking the blood of their victims in order to procreate. These aquatic flies have been called one of the most dangerous insects on the planet for their ability to transmit deadly diseases, among them malaria, yellow fever, typhus, encephalitis and West Nile virus. Luckily, only about 50 of them make themselves at home here in Missouri.

It takes as few as 10 days from the time a mosquito lays up to 400 eggs on the surface of standing water until her brood is a humming hoard of airborne, blood-seeking adults.

As humans, our current most effective defense against them — besides the diligent removal of breeding sites such as old tires and receptacles that trap rainwater from our yards — is repelling them by applying the synthetic chemical N,N-Diethyl-meta-toluamide (DEET) to our exposed surfaces. Developed by the U.S. Army for military use, DEET offers long-lasting protection from mosquitoes, but it also comes with issues of human toxicity.

And a study completed earlier this year by researchers at the University of Crete suggests that some mosquitoes grow less sensitive to DEET after a first exposure.

Twice in the last few weeks, I've been asked if there were plant-based solutions to the mosquito problem, and my research shows that there are some with merit.

But first, what doesn't work? Electronic bug zappers don't work against mosquitoes. The scented geranium Pelargonium citrosum, also known as citrosa geranium or the "mosquito plant," does not deter the little buzzers. Marigolds also have been touted to ward off mosquitoes, but only the Mexican marigold (Tagetes lucida) has some merit. Avon's Skin-So-Soft is not effective, and neither topical vanilla applications nor ingested garlic are going to hold mosquitoes at bay.

Citronella candles, scented with extracts from the tropical grass of the same name, are popularly used to discourage mosquitoes from joining the party, though the protection is fairly minimal. Geriniol candles, made with extracts from the plant Monarda didyma, are more effective.

It is the essential oils in plants that mosquitoes find distasteful, and these are not released unless the plant's leaves are crushed. In general, just growing mosquito non-friendly plants will not deter the blood-sucking insects. You must crush the leaves and rub them on your skin and clothing, or, if you have a big enough patch, you can crush and strew them underfoot to release the good stuff as you walk on them.

It is also possible to make infusions with the plants detailed below by crushing them, adding them to water and letting them sit — with an occasional shake — for a few days. Strain out the leaves, and put the solution in spray bottle for a little homemade mosquito-inhibiting spritz.

Monarda, also known as horsemint and bergamont, is the first plant that I can recommend as a mosquito non-friendly plant to grow in your garden. The cultivar known as "rose-scented" contains the highest concentrations of geraniol, which is also found in some natural commercial repellents.

My initial research on what mosquitoes don't like led me to buy a packet of catnip seeds (Nepeta cateria) the next time I passed by a seed rack. Researchers at the University of Iowa found that the essential oil in catnip, nepatalactone, is a highly effective repellent. I'm not certain how my cats will respond to a widespread use of this scented perennial herb, which is thought to stimulate receptors in a cat's brain that responds to its "happy" pheromones.

Lemon thyme (Thymus citriodorus) was found to be the best "crush and rub" plant to deter mosquitoes by researchers at the University of Guelph in Canada. A beautiful little culinary herb, it might be tough to grow enough for summer-long application, so you might want to try the somewhat invasive lemon balm (Melissa officinalis), also very off-putting to mosquitoes. Both perennial plants contain citronellal.

Following a "folklore" lead, researchers at the University of Mississippi found three chemicals in the leaves of the indigenous shrub American beautyberry (Calicarpa americana) — callicarpenal, intermedeol and spathulenol — that provide defense against mosquitoes, and two of them repel ticks, as well.

If you can't repel 'em, trap 'em. A recipe for a homemade baited mosquito trap is available by doing a search for "mosquito trap" at motherearthnews.com. Another version can be found by typing "soda bottle mosquito trap" into your search engine's browser.

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